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How to call a javascript function in HTML

Understanding the Basics

Before we delve into how to call a JavaScript function in HTML, it's essential to understand what these terms mean individually. JavaScript is a dynamic, high-level language, commonly used to enable interactive effects on websites. A function in JavaScript is a block of reusable code that performs a specific task.

HTML, on the other hand, stands for HyperText Markup Language. It's the standard language used to create web pages. Now that we've covered the basics, let's dive into the integration of JavaScript functions into HTML.

JavaScript Functions: What are they?

Imagine a function as a machine in a factory. You provide this machine with raw materials (these are your inputs or arguments), the machine then works on these materials (this is the process that happens inside the function), and finally, out comes a finished product (this is your output or return value).

In JavaScript, a function is defined using the function keyword, followed by a name, and a pair of parentheses (). The code to be executed by the function is placed inside curly braces {}.

function myFunction() {
  // code to be executed

Calling a JavaScript Function in HTML

To call a JavaScript function in HTML, we use event handlers. Think of event handlers as a notification system. When a specific event (like a click, a page load, or a mouse hover) occurs, these event handlers notify the JavaScript function, prompting it to run.

There are several ways you can call a JavaScript function in HTML. We'll explore the three most common methods.

1. Inline JavaScript

The first method is to call the JavaScript function directly within your HTML tags using event handlers. This method is known as inline JavaScript.

<button onclick="myFunction()">Click me</button>

In the above example, onclick is an event handler that listens for a mouse-click event. When the button is clicked, it triggers the myFunction().

2. Internal JavaScript

The second method is to place your JavaScript code within a <script> tag in your HTML file. This is called internal JavaScript. The <script> tag can be placed within the <head> or the <body> of the HTML document, but it is generally recommended to place it just before the closing </body> tag to improve page load speed.

  function myFunction() {
    alert("Hello, World!");

<button onclick="myFunction()">Click me</button>

In this example, when the button is clicked, it calls myFunction(), which then displays an alert box with the message "Hello, World!".

3. External JavaScript

The third method is to link an external .js file to your HTML document. This method is preferred when you have a large amount of JavaScript code, as it keeps your HTML document clean and easy to read.

Here's how you can link an external JavaScript file:

<script src="script.js"></script>

<button onclick="myFunction()">Click me</button>

And in your script.js file:

function myFunction() {
  alert("Hello, World!");

Again, when the button is clicked, it triggers myFunction(), which displays an alert box with the message "Hello, World!".

Things to Remember

When calling JavaScript functions in HTML, remember to match function names exactly as they are case-sensitive. Also, when using external JavaScript, ensure the file path is correctly specified.


In this post, we've explored how to call a JavaScript function in HTML. We've looked at three methods: inline, internal, and external JavaScript. While each has its advantages, the best method for you will depend on your specific needs and the complexity of your JavaScript code.

Remember, practice makes perfect. The more you experiment with calling JavaScript functions in HTML, the more comfortable and proficient you'll become. So, don't be afraid to experiment and happy coding!